I'm trying to make a raised bed out of planks but every time I nail one sid : Grows on You

Dorset, United Kingdom

I'm trying to make a raised bed out of planks but every time I nail one side, the other side comes undone -also should I make the wooden frame in situ, or on a flat surface and carry it over. I thought it would be a quick job but I've spent 2 + 1/2 hours so farand just have lots of sticking out nails - Help please !